1. Memory issue. You need enough memory during burning. Otherwise, the drive has to pick up data from hard drive more frequently which takes time.
2. Media. Some DVD media needs longer time to burn such as DVD+RW.
3. Battery: It is not advised to burn DVD using laptop battery. The computer slows the process to save power.
4. Software: If you burn video, some softeware has to render the file which takes longer time.